Feed direction dependent milling dynamics of an asymmetric flexible machining system

Asymmetric flexible machining system has been widely used in NC machining. In traditional milling dynamics model, the cutter feed direction is usually defined as parallel to its vibration DOF, while the nonparallel condition and its induced milling dynamics response are not deeply considered. This paper presents a general dynamics modeling method for asymmetric flexible machining systems. Firstly, to the best of the author's knowledge, a new dimension named feed direction is proposed, which is used to establish the generalized coupling relationship between the vibration displacement and the regenerative milling force, thus improve the applicability of the milling dynamics model and reduce the experimental workload compared with the traditional modeling. Secondly, through the theoretical and experimental research, it is shown that the asymmetric flexible machining system has a significant feed direction dependent characteristics, and implied the existence of high performance machining region with higher stability and low SLE by contrast with the symmetrical milling system and the traditional model. Finally, by controlling the feed direction angle, the milling parameters in roughing and finishing operation are optimized, and the machining efficiency has been greatly improved on the premise of stable cutting and machining accuracy at last.

Milling Dynamics and Propagation of Mechanically Activated Self-Sustaining Reactions

This work focuses on the propagation of mechanically activated self-sustaining reactions during the mechanical processing of powder in ball mills. We use a numerical model to reconstruct the dynamics of a single ball and powder particles inside the reactor of a SPEX Mixer/Mill 8000 under operational conditions. Taking advantage of the analytical description of the reactor swing, the equations of motion of ball and powder particles are solved numerically. The discrete element method is used to describe contacts. Reaction is ignited in an individual particle randomly selected among those compressed during an impact between ball and reactor. A simple kinetic law and a set of rules involving degree of chemical conversion and distance between particles are used to obtain a phenomenological description of the reaction propagation. We show that the propagation is significantly affected by reaction rate in individual particles, with other factors being less influential. We observe a strong coupling between the dynamics of powder particles and the reaction propagation.

Transient Vibration Analysis Method for Predicting the Transient Behavior of Milling With Variable Spindle Speeds

Variable spindle speed (VSS) technique is widely adopted for its effective suppression of chatter. However, heavy transient vibrations occur in practical machining operations although the stable machining parameters are selected according to the asymptotic stability analysis methods. In this paper, this problem is addressed through establishing a transient vibration analysis method to predict the transient behavior of VSS milling. Firstly, the discrete dynamical map of VSS milling is constructed, and the response to initial conditions (RTICs) and the response to external forcing (RTEF) can fully describe the general milling dynamics. On this basis, two transient vibration growth phenomena are found and proved that strong transient vibrations are induced by the transient growth of RTIC or RTEF. To fully predict the transient vibration growth phenomenon, the proposed method adopts the transient stability and receptivity analyses to evaluate RTIC and RTEF, respectively. Other than the existing methods, it gives a stability criterion based on both eigenvalues and nonnormal eigenvectors and considers the transient behavior to external excitation. Besides simulations, a real milling test in an existing work and VSS milling experiments are adopted for verification. The results show good agreement with the prediction of the proposed method.